Welding is a common method of fastening two pieces of metal or other material together. Generally, two surfaces to be joined are locally heated by a heat source to a molten state, causing molten material to flow into the gap between the surfaces. The molten material solidifies when the source of heat is removed to form a permanent bond joining the two surfaces together.
There are a variety of known methods of heating material to a molten state to form a weld. One common method is arc-welding, which generates the heat required for welding by passing a very high electrical current through the pieces to be welded. Because the material to be welded must be electrically conductive and because this method of welding is capable of generating very high temperatures, it is often the method of choice for joining pieces of metal such as steel or cast iron.
One pole of the electrical source (normally the negative or ground connection) is electrically connected to the work to be welded, while an electrode is connected to the other pole thereof. When the electrical source is activated, an extremely high electric current (150-2000 amperes, depending upon the particular electrical source used) causes the air in the gap between the work and the electrode to ionize and thus form an electrical arc when the electrode is brought into close proximity to the work. The part of the work exposed to the electrical arc is locally heated to a molten state by the very high electrical current flowing through it.
The shape of the electrode of an arc-welder must be of special design in order to facilitate both ionization of the air gap and accurate positioning and shaping of welds. The composition of the electrode is critical because it, too, is exposed to extremely high currents which could cause it to melt. Replaceable arc-welding rods are conventionally used as the electrode.
Conventional arc-welding rods are of two general types: consumable and non-consumable. Consumable welding rods have a melting temperature approximately equal to that of the work to be welded, and usually have somewhat the same metallurgical composition as that of the work (together with additives to produce welds with predetermined desirable properties). When an electrical arc ionizes the air gap between the work and welding rod, both the work and the tip of the consumable welding rod are heated to the molten state. The molten material at the end of the welding rod is used as filler metal to form part of the weld. Non-consumable welding rods, on the other hand, are composed of materials with extremely high melting points (such as carbon or tungsten). Non-consumable rods do not melt during the welding process and are used merely as inert electrodes from which electrical arcs may emanate.
Non-consumable welding rods are, however, subject to vaporization and oxidation due to exposure to the very high temperatures of welding, and thus are in fact eventually consumed (although much more slowly than the consumable rods). Oxidation is largely prevented by "shielding" the welding rod during welding by exhausting a quantity of inert gas (suitably helium, argon, helium-argon mixtures or carbon dioxide) around the tip of the rod. Even so, the rod tip still oxidizes slightly, and is subject to vaporization due to the extremely high temperatures present at the tip of the rod. Since the shape of the end of the rod is critical to the ability to easily form an arc and to control the direction of that arc once it is formed (e.g. so that welds may be precisely positioned and shaped), the working end of a non-consumable rod must therefore be periodically worked (e.g. sharpened) in order to maintain a point or other desired shape.
Conventionally, non-consumable tungsten arc-welding rods are in the form of thin rods of solid tungsten (available in various standard diameters from 1/16 to 3/16 of an inch) approximately 7 inches long. One end of the tungsten rod must be sharpened to a point before use so as to provide the welder with the ability to control the direction of the arc when formed and thus permit precise welding. Sharpening of the tungsten rod is conventionally accomplished by using a rotating abrasive grinding wheel such as a conventional bench grinding wheel or side grinding wheel. A pointed end with an even taper about the circumference of the welding rod is desirable so that the welding arc will extend axially from the tip of the rod when in use.
Welders will typically manually grasp the tungsten rod during its sharpening and thus will bring it into sharpening proximity with the rotating grinding wheel. This conventional sharpening practice is relatively dangerous because the rod will exhibit a tendency to slip out of contact with the wheel, causing potential serious bodily injury to the welder if his hands should strike the rotating wheel. Moreover, severe burns can result from grasping welding rods that have not yet cooled completely from the welding process. Because tungsten is a relatively expensive material, it is desirable to use as much of the welding rod as possible. Thus, it is often necessary to sharpen the end of relatively small length welding rod. It is extremely difficult for a welder to manually grasp such a short length of rod to accurately sharpen it and thus this factor also increases the danger of injury to the hands due to possible slippage of the rod on the grinding wheel. Moreover, it is extremely difficult to steady a short piece of welding rod to achieve a desired even-tapered point in accordance with conventional practices.
Fixtures for retaining rod-like workpieces so that the end of the workpiece may be easily worked are, of course, well known in the art. In this regard, the reader's attention is directed to the following list of patents (which is by no means exhaustive) so that further insight into the novel aspects of the present invention can be gleaned. Borzi (U.S. Pat. No. 2,551,721 issued May 8, 1951) discloses a fixture for retaining a bullet-shaped workpiece so that the end of the workpiece may be ground; Holcomb (U.S. Pat. No. 2,054,159 issued Sept. 15, 1936) discloses a handle member for retaining a pivot pin so that a conical bearing may be ground on the end of the pin; Stromgren (U.S. Pat. No. 1,873,067 issued Aug. 23, 1932) discloses a fixture for retaining a valve stem while the end of the valve stem is ground; Broscoff et al (U.S. Pat. No. 3,862,516 issued Jan. 28, 1975) discloses a vise for retaining the cap of a screw or bolt while the end of the screw or bolt is worked; Ernesto (U.S. Pat. No. 3,376,674 issued Apr. 9, 1968) discloses a fixture for retaining a punch while an angled surface is cut into it; Diesel et al (U.S. Pat. No. 1,430,063 issued Sept. 26, 1922) discloses a jig for retaining a lamp reflector for polishing.
As the reader will appreciate from careful consideration of the discussion which follows, the present invention is a novel device for retaining tungsten welding rods while they are being sharpened which permits easy and accurate shaping of the end of the rod without the associated dangers of physical injury to the welder presented by conventional sharpening techniques.